Researchers asked lunch and dinner customers at chain restaurants like McDonald's and Burger King to estimate their meals' total calories, and then tabulated actual calorie counts using the customers' bills. The results?

‘At least two-thirds of all participants underestimated the calorie content of their meals, with about a quarter underestimating the calorie content by at least 500 calories,' the study authors write.

Adults tended to underestimate their meals by about 175 calories, the same as children. Adolescents were more likely to underestimate by about 250 calories. Adults with a higher BMI were less likely to underestimate than their normal weight counterparts.

It's kinda interesting that higher BMI adults did a better job of estimating calories, when you might expect the opposite: that a failure to estimate calories accurately would actual explain the higher BMI. Maybe the direction of causation is the other way around: people who first develop higher BMIs then learn to estimate calories better than the average person, from reading food labels and deliberately trying to lose weight.

Subway sandwich restaurant diners were the most incorrect about the calories in their meals, consistently underestimating calories by 350 calories (adults) to 500 calories (adolescents). This is also not so surprising, given that Subway's marketing often stresses how fresh and healthy the food is, while the stores still dish up customer favorites full of multiple meats, cheeses, and creamy sauces.

The study had some limitations. In particular, many diners who the researchers approached refused to participate in the study, and they might have been better (or worse) calorie estimators than those diners who did choose to participate, for whatever reason. But the researchers had their own limitations. The conclusion they drew from the study was that more restaurants should display calorie counts clearly on their menus (only 20% of participating diners reported noticing any calorie counts). But it's not clear that calorie counts on menus have as dramatic an effect on people's choices as policy makers had hoped. The problem of estimating calories is unfortunately must easier to describe than to fix.